1. Field of the Invention
This invention relates to activators where both the forward and reverse linear movement force is supplied by springs.
2. Description of the Prior Art
U.S. Pat. No. 954,682 patented Apr. 12, 1910 to A. A. Low et al discloses electrothermal means for producing mechanical movement. This movement is achieved by having two circuits in mechanical opposition attached at a common place on a pivotally mounted arm. Each circuit has a current carrying thermally expansible member held in position by a spring. Movement is obtained by passing electric current through one of the two circuits causing that wire to expand and the spring to contract. This action allows the heated member arm to swing towards the unheated arm.
U.S. Pat. No. 3,016,691 patented Jan. 16, 1962 by G. Asakawa et al discloses a device for converting electrical energy into translational mechanical movement. This movement is achieved by filling an insulated cylinder with a mixture of finely divided electrically conductive particles dispersed in a thermally expansible non conductor of electricity. An electrode in contact with the mixture is attached at the closed end of the cylinder and the other electrode is attached to an electrically conductive piston inserted into the open end of the cylinder. As the current flows through the mixture, the mixture expands, forcing the piston out.
U.S. Pat. No. 3,163,732 patented Nov. 19, 1974 to C. D. Hickling discloses an electric switch which is actuated (pushed to the closed position) by an arm which is pulled down across the switch. The arm is moved into position by the heating of a Nitinol.TM. or similar alloy wire which forms a spring. When the spring cools, the lever is moved back to the off position by a leaf expansion spring. The switch is used for thermostats and the like.
U.S. Pat. No. 4,463,560 patented Aug. 7, 1984 to A. H. Greenleaf et al discloses a thermal actuator apparatus for adjusting the position of a surface as a function of temperature. The adjustment is achieved by the use of springs having different thermoelastic coefficients between the two planes. Together they are in a balanced equilibrium condition but individually one is pulling in and the other is pushing out. One of the springs is made of an alloy while the other is made of stainless steel.
The need for a linear actuator has been recognized and many attempts have been made to provide a solution. However, each device offered has required one type of mechanism to extend the actuator and a different means for returning the actuator to the starting position. Furthermore, many of these devices required more space than desired due to their clumsy mechanisms. Thus it is an object of this invention to provide an actuator which employs the same type of means for movement in each direction. It is another object of this invention to provide a more compact actuator requiring less space for and during operation. Still other objects will be apparent to those skilled in the art upon reference to the following detailed description.